Restricting Matrix Multiplication

[egekorkan]

In the current common definitions proposal, it is possible to have a TD like this:

    {
      "@context": "https://www.w3.org/ns/wot-next/td",
      "title": "valid-test-multi-protocol",
      "formDefinitions": {
        "http": {
          "base": "https://192.168.1.10:8080",
          "contentType": "application/json",
          "security": {
            "scheme": "nosec"
          }
        },
        "coap": {
          "base": "coap://[2001:DB8::1]/mything",
          "contentType": "application/cbor",
          "security": {
            "scheme": "nosec"
          }
        }
      },
      "formDefaults": ["http", "coap"],
      "properties": {
        "prop1": {
          "type": "string",
          "forms": [
            {
              "href": "props/prop1"
            },
            {
              "href": "properties/prop1"
            }
          ]
        }
  }
}

There would be 4 forms in total when expanded, where two single dimensional arrays get multiplied like in matrix multiplication:

          "forms": [
            {
              "href": "https://192.168.1.10:8080/props/prop1",
              "contentType": "application/json",
              "security": {
                "scheme": "nosec"
              },
              "op": ["readproperty", "writeproperty"]
            },
            {
              "href": "coap://[2001:DB8::1]/mything/props/prop1",
              "contentType": "application/cbor",
              "security": {
                "scheme": "nosec"
              },
              "op": ["readproperty", "writeproperty"]
            },
            {
              "href": "https://192.168.1.10:8080/properties/prop1",
              "contentType": "application/json",
              "security": {
                "scheme": "nosec"
              },
              "op": ["readproperty", "writeproperty"]
            },
            {
              "href": "coap://[2001:DB8::1]/mything/properties/prop1",
              "contentType": "application/cbor",
              "security": {
                "scheme": "nosec"
              },
              "op": ["readproperty", "writeproperty"]
            }
          ]

We can make a choice to restrict this, i.e. if formDefaults is present (and is an array), the forms in affordances MUST be a single item array. @benfrancis this should be also in the "surprising" category of behavior to you?

[egekorkan]

TD Call: we will address this before transitioning the proposal to accepted. This "surprise" effect will hinder the usage/adoption of the feature. Decision would be:

• If you have a TD use case like the expanded TD above, you should not use this feature.
• In other words, if formDefaults is used, the forms in affordances must be a single item array.

Note:

• This will complicate the TD validation

[egekorkan]

If there is this kind of TD, one way to model it is by not using formDefaults but only formDefinitions and then refer to it multiple times. Will add a valid test case